It is known in the automotive industry that vehicle drag is one of the greatest design challenges to be overcome. A moving vehicle displaces surrounding air while in motion. The resulting resisting force is referred to as aerodynamic drag. Automobile designers seek to reduce the amount of drag on a vehicle insofar as this force has an increasingly detrimental impact on vehicle fuel economy as the vehicle's speed is increased. As vehicle velocity increases, the amount of vehicle aerodynamic drag as a result of the increased airflow around the vehicle increases. As aerodynamic drag increases, more energy is required to move the vehicle.
It is also known in the automotive industry that the frontal area of the vehicle and the drag coefficient are the two main characteristics that determine aerodynamic drag. The drag coefficient indicates the degree to which a vehicle resists travel through surrounding air. Accordingly, to increase efficiency, designers are required to reduce the vehicle's drag coefficient. This goal has been achieved in part by removing such external components as mud flaps, roof racks and antennae while making necessary components, such as mirrors and front bumpers, more aerodynamic.
While many of these steps have provided a degree of satisfaction in achieving reduction of the drag coefficient related to vehicle body design, reducing the vehicle's drag coefficient generated by the underside of the vehicle is more challenging. To this end, some success has been achieved by providing a dynamic system whereby the body of the vehicle is lowered relative to the wheels, thereby restricting the amount of air that is allowed to pass between the vehicle and the roadway. Another strategy is to provide an under tray that covers all or some of the underside of the vehicle, thus preventing air from being trapped. Both of these efforts achieve some success in reducing the vehicle's drag coefficient. However, the latter approach requires relatively expensive frame features while the former approach, while being common in racing vehicles, is impractical for the typical family vehicle for several reasons, including vehicle ground clearances under normal operations.
As an alternative to lowering the vehicle during operation or providing an under tray, vehicle designers realize that drag reduction of underbody components may be dealt with on a component level. One such approach has been to consider a redesign of all or part of the vehicle's exhaust components. For example, U.S. Pat. No. 9,464,557, issued on Oct. 11, 2016, for MUFFLER SHIELD AND MUFFLER ASSEMBLY EMPLOYING THE SAME and assigned to the same assignee as the present application and incorporated by reference herein, provides a muffler shield including a shield body that extends in a longitudinal direction and defines a middle portion positioned between first and second side portions along a transverse direction. A cross-section of the middle portion and at least one of the first and second side portions respectively define a middle profile and a side profile shorter than the middle profile.
While this reference represents an improvement in the reduction of a vehicle's drag coefficient by reducing aerodynamic turbulence associated with the muffler, other approaches to reducing vehicle drag related to the muffler are possible.